Leads implanted in or about the heart have been used to reverse certain life threatening arrhythmias, or to stimulate contraction of the heart. Electrical energy is applied to the heart via the leads to return the heart to normal rhythm. Leads have also been used to sense in the atrium or ventricle of the heart and to deliver pacing pulses to the atrium or ventricle.
Cardiac pacing may be performed by the transvenous method or by leads implanted directly onto the epicardium. Permanent transvenous pacing is performed using a lead positioned within one or more chambers of the heart. One or more leads may be positioned in the ventricle or in the atrium through a subclavian vein, and the lead terminal pins are attached to a pacemaker, which is implanted subcutaneously.
The leads include an outer insulative lead body for electrically insulating the conductor, and allowing only the electrodes to make electrical contact with the body tissue. The insulation of the conductor must be reliable, to prevent inadvertent shorting of the conductor. The outer insulation affects the several aspects of the lead structure, for example, lead flexibility and abrasion resistance, and the outer dimensions of the lead body. It is preferable that the lead is flexible since, the more flexible a lead is, the less trauma is induced to the patient as a result of lead pressure. Furthermore, flexibility is an important consideration in light of the repeated movements of the heart, and also the tortuous path through which the lead is inserted. In addition, the outer body must be resistant to abrasive wear, for example, in the event that the lead rubs against another lead, implanted device, or anatomical structure while the lead is in use after it is implanted within a patient.
Some leads incorporate silicone as an insulator for the conductor. However, while silicone is a flexible and biostable material, silicone has poor tensile and wear characteristics. Furthermore, silicone has a high coefficient of friction, which is a drawback, for example when two leads are placed within the patient, or when silicone is used in proximity with moving parts.
Another consideration is the lead body diameter. Physicians prefer smaller leads because a smaller introducer can be used, and a smaller incision for the introducer is used. Furthermore, smaller leads are necessary when the relevant therapies require two or more leads to be implanted.
Accordingly, there is a need for a lead, which has improved flexibility. What is also needed is a lead having a smaller outer diameter that does not sacrifice insulation.